When internal combustion of an equipment is caused by internal short circuits or other reasons, effective measures need to be taken to prevent flames from spreading to the outside of the equipment so as to avoid unnecessary risks. Conventional practice is to connect a thermal fuse in a power supply circuit of a cooling fan of the equipment in series. While internal combustion of the equipment is happening, internal temperature is high enough to melt the thermal fuse so as to turn off the cooling fan. One effect is to prevent air convection caused by continuous work of the fan, reduce supply of internal oxygen and make the combustion not continue any loner. Another effect is to prevent the fan from blowing flames out of the equipment and causing objects around to be burnt.
As shown in FIG. 1, which is a diagram illustrating a regularly adopted solution for overheat protection circuit in the prior art, the working mechanism is to connect a thermal fuse into the power supply circuit of a monitored unit in series. Thermal fuses F1, F2 are melted to cut off the power supply of the monitored unit when the temperature is high enough to avoid the harms caused by overheat. The aim of using the parallel connection design of the thermal fuses F1, F2 is to prevent mis-operation caused by failure of one of the thermal fuses. The thermal fuses are made into a small module and installed on a structure supporting frame of equipment via wires. The monitored unit shown in the figure is a fan.
In the solution of the prior art, due to lack of any automatic detecting measure to report the failure of the thermal fuse and reminding a maintainer for timely replacement when one of the thermal fuses fails due to other reasons (for example, fails during production welding), a fan may be turned off incorrectly if other thermal fuses also fail because of other reasons except over temperature (for example, a failure of aging). This may result in a quite high internal temperature without cooling by the fan and cause damage to the equipment. Furthermore, a service may be abnormal or even collapse. Therefore, the solution shown in FIG. 1 has poor maintainability and testability. In addition, the thermal fuse monitors the power supply of the fan which is strong power. The thermal fuse module is regularly installed on the structure support of the equipment and the support is connected to a protection ground (PGND) of the equipment. Therefore, there are safety specification requirements on the wires of the power supply and the PGND of the support. At the same time, shell and pins of some thermal fuses are equipotential. In other words, the housing and the power supply are also equipotential when the pins of the thermal fuse are connected to the power supply. Therefore, there are safety specification requirements on the shell of the thermal fuses and the PGND of the structure element of the equipment. A short circuit between the PGND and the power supply may be easily caused in the case of improper processing.